1. Field of the Invention
This invention relates to a method of mounting valve seats in a butterfly valve including adjusting arcuate seat parts adapted to contact a valve body peripherally when the valve is closed, in respect of positions of end surfaces thereof, by screwing first bolts into a valve housing, each of the first bolts having a tapered tip end approximately in a cone shape to fit into a tapered hole defined on the seat parts, and adjusting the seat parts towards or away from the valve body by screwing a multiplicity of second bolts arranged peripherally of the valve body relative to the valve housing.
2. Description of the Prior Art
For maintenance of a good leakproof condition in a butterfly valve, it is essential that the valve seats are made adjustable to have the end surfaces thereof suitably disposed relative to the valve stem or seal members surrounding the valve stem, and the inner surfaces thereof movable towards and away from the periphery of the valve body.
Part of the prior art arrangement is illustrated in FIG. 8. As seen, a valve seat 33 is formed with a tapered hole h, and a valve housing carries first bolts 31 each having a tapered tip end j to fit into the hole h. Each first bolt 31 has an axis P5 slightly displaced from an axis P6 of tapered hole h by a small amount l towards an end of the valve seat 33. The first bolt 31 is screwed into the housing 32 to cause a camming action between the tapered hole h and the tapered tip end j so as to adjust the position of the end surface of the valve seat using peripherally acting components of force thus created. In addition to such provision, a multiplicity of second bolts are provided in the peripheral direction of the valve body. By screwing these second bolts relative to valve housing 32, valve seat 33 is adapted to move towards or away from the valve body.
Pressing forces to act on valve seat 33 in the vicinity of the first bolts 31 comprise only the components of force created in the screwing direction of the first bolts 31 when the positions of the ends of the valve seat are adjusted. Such pressing forces depend largely on an amount of the seat end adjustment. Even if the first bolts 31 are tightened with a torque equal to the torque for tightening the second bolts, the pressing forces of the first bolts 31 are bound to be smaller. This results in inequality in the pressures in the peripheral direction of the valve seat against the periphery of the valve body, and in liability to fluid leakage. Such is the disadvantage of the known arrangement.